Do you homeschool year round? If so, do you use the curriculum you have used all year, or do you and your children pick something fresh and new?
I am certain that most homeschooling families school through the summer to a certain extent. Even traditional schooling families school in the summer - it just looks different. Family hikes, visits to the zoo, summer reading programs, summer bridge books, building projects, gardening and more - this is school in the summer. Sure, some kids (like my own), need to keep the math going for retention, but generally, summer school can be what you make it.
Have you considered asking your child what they might like to learn about over the summer? Maybe they have a favorite book series, or are needing a new book series. The Beforever books by American Girl and the I Survived series published by Scholastic are excellent summer reading options. There are short term unit studies that use these books as a spine - See Girls of American History and Historical Stories of Survival. These units are an excellent way for your kids to pick up some new hobbies, to make family memories over the summer and learn about amazing times in history and science discovery.
I can't tell you which units until the sale starts - But I can tell you that there are some units for each of these collections in the Homeschool Resources Bundle Sale